The bureau assisted in the investigations of the deaths last Spring of Nathaniel Holmes, Cynthia Day and Miranda Schaup-Werner.

Schaup-Werner, a 41-year-old Pennsylvania resident, died in May at the Grand Bahia Principe in La Romana, as did the 63-year-old Holmes, and the 49-year-old Day, a couple from Maryland.

“Our condolences and sympathy go out to the families during this difficult time,” the State Department official said in a statement, adding that relatives of the deceased have been informed of the FBI test results.

There was no immediate response from the family members.

The State Department official said the deaths were tragic but called them unrelated, isolated cases. The US has not seen an increase in the number of deaths of American citizens in the Dominican Republic, the official said.

Schaup-Werner died in her hotel room after having a drink from the minibar, family spokesman Jay McDonald told CNN affiliate WFMZ. She suffered a heart attack, pulmonary edema and respiratory failure, a preliminary autopsy cited by the Attorney General’s Office of the Dominican Republic showed.

Holmes and Day were found dead days later in their hotel room on May 30. Both had internal bleeding, including in their pancreases, according to Dominican authorities. Holmes had an enlarged heart and cirrhosis of the liver — both signs of significant pre-existing disease, the Dominican authorities said. Day had fluid in her brain, they said.

Holmes and Day also had fluid in their lungs, Attorney General Jean Alain Rodriguez Sanchez’s office said in a statement at the time.

The Dominican Republic is one of the Caribbean’s top tourism destinations, with more than 6 million stopover tourists last year, including 2.2 million Americans, according to the Caribbean Tourism Organization.